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4

Work done is said to be zero, when

A. Some force acts on a body, but displacement is zero

B. No force acts on a body but some displacement takes place

C. Either (A) or (B)

D. None of the above

Correct Answer :

C. Either (A) or (B)


Related Questions

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4

A circular hole of 50 mm diameter is cut out from a circular disc of 100 mm diameter as shown in the below figure. The centre of gravity of the section will lie

A. In the shaded area

B. In the hole

C. At O

D. None of these

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4

Which of the following do not have identical dimensions?

A. Momentum and impulse

B. Torque and energy

C. Torque and work

D. Moment of a force and angular momentum.

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4

In ideal machines

A. Mechanical advantage is greater than velocity ratio

B. Mechanical advantage is equal to velocity ratio

C. Mechanical advantage is less than velocity ratio

D. Mechanical advantage is unity

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4

The moment of inertia of a sphere of mass m and radius r, about an axis tangential to it, is

A. 2mr2/3

B. 2mr2/5

C. 7mr2/3

D. 7mr2/5

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4

The resultant of the following three couples 20 kg force, 0.5 m arm, +ve sense 30 kg force, 1 m arm, -ve sense 40 kg force, 0.25 m arm, +ve sense having arm of 0.5 m will be

A. 20 kg, -ve sense

B. 20 kg, + ve sense

C. 10 kg, + ve sense

D. 10 kg, -ve sense

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4

A projectile is fired at an angle θ to the vertical. Its horizontal range will be maximum when θ is

A.

B. 30°

C. 45°

D. 60°

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4

The forces, whose lines of action are parallel to each other and act in the same directions, are known as

A. Coplanar concurrent forces

B. Coplanar non-concurrent forces

C. Like parallel forces

D. Unlike parallel forces

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4

According to Lamis theorem

A. The three forces must be equal

B. The three forces must be at 120° to each other

C. The three forces must be in equilibrium

D. If the three forces acting at a point are in equilibrium, then each force is proportional to the sine of the angle between the other two

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4

The centre of gravity of a quadrant of a circle lies along its central radius (r) at a distance of

A. 0.5r

B. 0.6 r

C. 0.7 r

D. 0.8 r

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4

Which of the following is not the unit of power?

A. kW (kilowatt)

B. hp (horse power)

C. kcal/sec

D. kcal/kg sec

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4

The friction experienced by a body, when in motion, is known as

A. Rolling friction

B. Dynamic friction

C. Limiting friction

D. Static friction

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4

Varingon's theorem of moments states that if a number of coplanar forces acting on a particle are in equilibrium, then

A. Their algebraic sum is zero

B. Their lines of action are at equal distances

C. The algebraic sum of their moments about any point in their plane is zero

D. The algebraic sum of their moments about any point is equal to the moment of their resultant force about the same point.

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4

If a suspended body is struck at the centre of percussion, then the pressure on die axis passing through the point of suspension will be

A. Maximum

B. Minimum

C. Zero

D. Infinity

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4

The unit of force in S.I. system of units is

A. Dyne

B. Kilogram

C. Newton

D. Watt

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A semicircular disc rests on a horizontal surface with its top flat surface horizontal and circular portion touching down. The coefficient of friction between semi circular disc and horizontal surface is μ. This disc is to be pulled by a horizontal force applied at one edge and it always remains horizontal. When the disc is about to start moving, its top horizontal force will

A. Remain horizontal

B. Slant up towards direction of pull

C. Slant down towards direction of pull

D. None of the above

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4

Which of the following is not a vector quantity?

A. Weight

B. Velocity

C. Acceleration

D. Force

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4

The moment of inertia of a square of side a about its diagonal is

A. a2/8

B. a3/12

C. a4/12

D. a4/16

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4

The ratio of static friction to dynamic friction is always

A. Equal to one

B. Less than one

C. Greater than one

D. None of these

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4

The acceleration of a body sliding down an inclined surface is

A. g sinθ

B. g cosθ

C. g tanθ

D. None of these

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4

If rain is falling in the opposite direction of the movement of a pedestrian, he has to hold his umbrella

A. More inclined when moving

B. Less inclined when moving

C. More inclined when standing

D. Less inclined when standing

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4

Angle of friction is the

A. Angle between normal reaction and the resultant of normal reaction and the limiting friction

B. Ratio of limiting friction and normal reaction

C. The ratio of minimum friction force to the friction force acting when the body is just about to move

D. The ratio of minimum friction force to friction force acting when the body is in motion

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4

One kg force is equal to

A. 7.8 N

B. 8.9 N

C. 9.8 N

D. 12 N

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4

The coefficient of friction depends upon

A. Nature of surfaces

B. Area of contact

C. Shape of the surfaces

D. All of the above

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4

Dynamic friction as compared to static friction is

A. Same

B. More

C. Less

D. May be less of more depending on nature of surfaces and velocity

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4

Moment of inertia of a circular section about its diameter (d) is

A. πd3/16

B. πd3/32

C. πd4/32

D. πd4/64

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4

The velocity ratio for the first system of pulleys is (where n is the number of pulleys.)

A. n

B.

C. 2n

D. 2n - 1

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4

The moment of inertia of a thin rod of mass m and length l, about an axis through its centre of gravity and perpendicular to its length is

A. ml2/4

B. ml2/ 6

C. ml2/8

D. ml2/12

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4

The time of flight (t) of a projectile on an upward inclined plane is (where u = Velocity of projection, α = Angle of projection, and β = Inclination of the plane with the horizontal.)

A. t = g cos β/2u sin (α - β)

B. t = 2u sin (α - β)/g cos β

C. t = g cos β/2u sin (α + β)

D. t = 2u sin (α + β)/g cos β

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4

When trying to turn a key into a lock, following is applied

A. Coplanar force

B. Non-coplanar forces

C. Moment

D. Couple

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4

The C.G. of a right circular solid cone of height h lies at the following distance from the base

A. h/2

B. J/3

C. h/6

D. h/4